It was probably I you remember, I had one Aptus 75 that started to behave erratically below like +15C, I then paid for a full E-box replacement (everything except the sensor unit) so I got a virtually new Aptus, which worked better but still started to behave erratically below +7C. Asking around among other Aptus users on the forums I found a few that had problems above +30C and below freezing (which really hadn't reported about it until I explicitly asked), as well as many users that had no problems.
After a loooooong history with Leaf/Phase One support and non-existent dealer support here in Sweden (it was very difficult to get adequate help) I finally got a complete replacement unit, and that worked without issues in -30C. The really poor support I got from dealer/Leaf until top level management finally stepped in made my case sort of a soap opera in this forum, so I guess many have some memory of it.
Leaf themselves or dealers have never explicitly stated that the Aptus is less reliable than other backs, but I've seen statements like "if you need reliability you should get a P+ series" and other minor indications that the dealers actually know about that it can have issues.
My conclusion from other user's reports, my own experience and subtle indications from dealer statements is that there is likely some considerable
sample variation in the Aptus series, that is some backs have issues, others don't. Do I know 100% sure that this is the case? No. The other users could have had bad luck and I even some extra bad luck. I don't have any official statistics so I don't know if it's 1 out of 10 that has problems or 1 out of 100, but I find it highly likely that this is the case so when I consider an Aptus I prefer knowing if that particular instance have been used in the type of conditions I need it to work in, that is -30C. I'm not even sure if dealers really have full understanding of how reliable this back in these conditions as it's not very typical use case to shoot these medium format backs in tough outdoor conditions. Studio work is the traditional use case and still the most common I imagine. Perhaps it's only 1 out of 10 backs or even less that ever faces freezing temperatures? If that is the case and 25% has issues in cold weather then only 0.1 * 0.25 = only 1 out of 40 users will experience problems, and hence you won't hear about it often despite that it's high risk for those users that actually do shoot in these conditions. Had I shot my first back in room temperature only I would have never discovered any issue with it.
In any case I'm prepared to make a bet. If we shoot 50 Aptus backs in -30C and 50 Phase One P+ backs in the same condition, I can almost assure you that some of those Aptus backs will start behaving erratically after 30 minutes or so, certainly not all of them but I would think more than 5 of them maybe as much as half, I don't know, while probably none of the P+ will have problems. Of course this can never be tested for real, but just as an example of that I think Aptus means a raised risk, but not guarantee, that you can have issues in cold weather.
I have shot with older Hasselblad backs which had fans in very cold conditions and they worked just fine, as well as my latest Aptus, so I don't think the fan is a problem as such. If the board just have all components with top quality properly mounted then it will work out fine, so I don't think you should consider doing anything special with the fan. What you need is a "good copy" of the Aptus. If it's bad I don't think any fan trickery will solve the problem, I mean my two bad copies started to behave erratically below room temperature but
above freezing.
The fan is open straight into the electronics (just as the CF bay door), but the sensor unit itself is separate and quite well sealed. In this thread at getdpi
http://www.getdpi.com/forum/medium-format-systems-and-digital-backs/52991-aptus-internal-battery.html you can find photos where an Aptus back is dismantled and put together again (to change clock battery) which quite well show what's sealed and not. You should surely avoid getting water into the open vents.
I eventually switched to Hasselblad not because I was unhappy with the Aptus (the good copy I finally got worked very well in very cold conditions) but because the Hasselblad had the Kodak 50 megapixel sensor which is the best you can get for the Schneider Digitar wides I'm using on my tech cam. I could certainly get an Aptus again, but not without either checking that the previous owner had used it successfully in cold weather or if bought through a dealer get some sort of guarantee that I could return it if it should start behaving erratically in the cold. With the Hassies and Phase Ones and indeed the newer Leafs (Credo) the likelihood of issues is so low that I'm prepared to take the risk just as with a pro DSLR.
As you surely know all backs and most cameras are only rated to 0C, so you are dependent on goodwill if you get failures below that. High quality electronics works well way beyond spec so we're used to not really look into it we just assume that they work, but if you do get issues that no-more-than-0C-guarantee will jump at you. It's a bit like "weather sealing", if you get water damage issues it's the manufacturer that decides what's within spec or not. When dealing with the support when I got issues they clearly stated that they would not replace anything if it failed at -1C as they only guaranteed 0C, but I was "fortunate" enough that my backs failed in +7 - +15C.
This is strictly a user-to-user advice share. I'm not into trash talking Leaf, but as I suspect that there are issues I would tell my fellow user that, and I hope the above gives some insight into why I'm a bit more suspicious about the Aptus series than others, without the possibility to 100% sure know if there is a specific issue or not.
